A magnetic bearing uses a magnetic force to levitate a rotor in the air relative to a stator so that there is no mechanical contact between the rotor and the stator. Compared with the traditional rolling bearings, sliding bearings and the like, the magnetic bearing has a rotor that can operate to a very high speed, and thus is often used in high-speed, ultra-high-speed applications, such as some high-speed, ultra-high-speed machines. In this kind of machines, the magnetic bearing is a very critical component, once a magnetic levitation system fails, a magnetic levitation product cannot start the levitation and cannot operate normally as a result, which often results in production losses. Therefore, a corresponding protective device needs to be configured when the magnetic bearing is designed.
Typically, the structure of an axial magnetic bearing with a protective device in the prior art is shown in FIG. 3. The axial magnetic bearing includes a front axial iron core 31, a front axial bearing control coil 32, a front axial protective bearing 33, a thrust disc 34, a back axial protective bearing 35, a back axial bearing control coil 36, a back axial iron core 37 and optical axis 38. The protection principle of the protective device of the axial magnetic bearing is mainly as follows: a spacing gap is formed between a right end face of the front axial protective bearing 33 and a left end face of the thrust disc 34 as well as between a right end face of the thrust disc 34 and a left end face of the back axial protective bearing 35, and the spacing gap is smaller than the working gap of the axial magnetic bearing (i.e., the gap between a right end face of the front axial iron core 31 and the left end face of the thrust disc 34, and the gap between a right end face of the thrust disc 34 and the back axial iron core 37). When the thrust disc 34 rotates to work, the left end face of the thrust disc 34 generates frictional contact with the right end face of the front axial protective bearing 33, and the right end face of the thrust disc 34 generates frictional contact with the left end face of the back axial protective bearing 35 so as to prevent ablation and damage to each of the axial iron cores due to friction with the thrust disc.
In the technical solution, the protection gap between each axial protective bearing and the thrust disc and the working gap between each axial iron core and the thrust disc depend entirely on the assembly accuracy and the processing accuracy and cannot be directly adjusted, so that the product qualification rate is difficult to control, the quality flexibility is poor, and the thrust disc needs to be dissembled and assembled for multiple times during indirect adjustment, in this way, the magnitude of interference of the thrust disc is reduced, and potential safety hazards are caused. Meanwhile, in the technical solution, the front axial protective bearing 33 is assembled with the front axial iron core 31 by an interference fit, and the back axial protective bearing 35 is assembled with the back axial iron core 37 by an interference fit, and after the axial protective bearings 33, 35 are worn, the whole axial magnetic bearing becomes useless and cannot be used again, thus bringing great losses and inconvenience to the product maintenance.